A bioassay for Lafora disease and laforin glucan phosphatase activity

Dissolution-Enhanced Luminescence Enhanced Digital Microfluidics Immunoassay for Sensitive and Automated Detection of H5N1

Protein bioassay is a critical tool for the screening and detection of protein biomarkers in disease diagnostics and biological applications. However, the detection sensitivity and system automation of current immunoassays do not meet the emerging demands of clinical applications. Here, we developed a dissolution-enhanced luminescence-enhanced digital microfluidics immunoassay (DEL-DMF), which significantly improves the sensitivity and automation of the protein bioassay. In DEL-DMF, the sample and reagent droplets are controlled to complete the processes of sample transport, immunoreaction, and buffer washing, which not only minimizes sample consumption to 2 μL and enhances the binding efficiency of immunoreaction but also streamlines all the procedures and simplifies the process of immunoassay. Moreover, dissolution-enhanced luminescence using NaEuF₄ NPs as nanoprobes boosts the fluorescence and increases the sensitivity of the bioassay. We demonstrate the enhanced analytical performance of our DEL-DMF immunoassay to detect H5N1 hemagglutinin in human serum and saliva. A limit of detection of 1.16 pM was achieved in less than 0.5 h with only 2 μL sample consumption. Overall, our DEL-DMF immunoassay combines the merits of the microfluidics platform and dissolution-enhanced luminescence, thus affording superior detection sensitivity and system automation for protein biomarkers. This novel immunoassay microsystem holds great potential in clinical and biological applications.

A novel gene therapy for neurodegenerative Lafora disease via EPM2A-loaded DLinDMA lipoplexes

Aim: To develop novel cationic liposomes as a nonviral gene delivery vector for the treatment of rare diseases, such as Lafora disease - a neurodegenerative epilepsy. Materials & methods: DLinDMA and DOTAP liposomes were formulated and characterized for the delivery of gene encoding laforin and expression of functional protein in HEK293 and neuroblastoma cells. Results: Liposomes with cationic lipids DLinDMA and DOTAP showed good physicochemical characteristics. Nanosized DLinDMA liposomes demonstrated desired transfection efficiency, negligible hemolysis and minimal cytotoxicity. Western blotting confirmed successful expression and glucan phosphatase assay demonstrated the biological activity of laforin. Conclusion: Our study is a novel preclinical effort in formulating cationic lipoplexes containing plasmid DNA for the therapy of rare genetic diseases such as Lafora disease.

Identification and characterization of ChlreSEX4, a novel glucan phosphatase from Chlamydomonas reinhardtii green alga

Chlamydomonas reinhardtii is the best known unicellular green alga model which has long been used to investigate all kinds of cellular processes, including starch metabolism. Here we identified and characterized a novel enzyme, ChlreSEX4, orthologous to glucan phosphatase SEX4 from Arabidopsis thaliana, that is capable of binding and dephosphorylating amylopectin in vitro. We also reported that cysteine 224 and tryptophan 305 residues are critical for enzyme catalysis and substrate binding. Furthermore, we verified that ChlreSEX4 gene is expressed in vivo and that glucan phosphatase activity is measurable in Chlamydomonas protein extracts. In view of the results presented, we suggest ChlreSEX4 as a functional phosphoglucan phosphatase from C. reinhardtii. Our data obtained so far contribute to understanding the phosphoglucan phosphatases evolutionary process in the green lineage and their role in starch reversible phosphorylation. In addition, this allows to position Chlamydomonas as a potential tool to obtain starches with different degrees of phosphorylation for industrial or biotechnological purposes.

A novel EPM2A mutation yields a slow progression form of Lafora disease

Lafora disease (LD, OMIM 254780) is a rare disorder characterized by epilepsy and neurodegeneration leading patients to a vegetative state and death, usually within the first decade from the onset of the first symptoms. In the vast majority of cases LD is related to mutations in either the EPM2A gene (encoding the glucan phosphatase laforin) or the EPM2B gene (encoding the E3-ubiquitin ligase malin). In this work, we characterize the mutations present in the EPM2A gene in a patient displaying a slow progression form of the disease. The patient is compound heterozygous with Y112X and N163D mutations in the corresponding alleles. In primary fibroblasts obtained from the patient, we analyzed the expression of the mutated alleles by quantitative real time PCR and found slightly lower levels of expression of the EPM2A gene respect to control cells. However, by Western blotting we were unable to detect endogenous levels of the protein in crude extracts from patient fibroblasts. The Y112X mutation would render a truncated protein lacking the phosphatase domain and likely degraded. Since minute amounts of laforin-N163D might still play a role in cell physiology, we analyzed the biochemical characteristics of the N163D mutation. We found that recombinant laforin N163D protein was as stable as wild type and exhibited near wild type phosphatase activity towards biologically relevant substrates. On the contrary, it showed a severe impairment in the interaction profile with previously identified laforin binding partners. These results lead us to conclude that the slow progression of the disease present in this patient could be either due to the specific biochemical properties of laforin N163D or to the presence of alternative genetic modifying factors separate from pathogenicity.

Identification and analysis of OsttaDSP, a phosphoglucan phosphatase from Ostreococcus tauri

Ostreococcus tauri, the smallest free-living (non-symbiotic) eukaryote yet described, is a unicellular green alga of the Prasinophyceae family. It has a very simple cellular organization and presents a unique starch granule and chloroplast. However, its starch metabolism exhibits a complexity comparable to higher plants, with multiple enzyme forms for each metabolic reaction. Glucan phosphatases, a family of enzymes functionally conserved in animals and plants, are essential for normal starch or glycogen degradation in plants and mammals, respectively. Despite the importance of O. tauri microalgae in evolution, there is no information available concerning the enzymes involved in reversible phosphorylation of starch. Here, we report the molecular cloning and heterologous expression of the gene coding for a dual specific phosphatase from O. tauri (OsttaDSP), homologous to Arabidopsis thaliana LSF2. The recombinant enzyme was purified to electrophoretic homogeneity to characterize its oligomeric and kinetic properties accurately. OsttaDSP is a homodimer of 54.5 kDa that binds and dephosphorylates amylopectin. Also, we also determined that residue C162 is involved in catalysis and possibly also in structural stability of the enzyme. Our results could contribute to better understand the role of glucan phosphatases in the metabolism of starch in green algae.

Assessing the Biological Activity of the Glucan Phosphatase Laforin

Glucan phosphatases are a recently discovered family of enzymes that dephosphorylate either starch or glycogen and are essential for proper starch metabolism in plants and glycogen metabolism in humans. Mutations in the gene encoding the only human glucan phosphatase, laforin, result in the fatal, neurodegenerative, epilepsy known as Lafora disease. Here, we describe phosphatase assays to assess both generic laforin phosphatase activity and laforin's unique glycogen phosphatase activity.